Fix qmake -r by moving load(qt_parts) to the end of the project

This is an issue for non-developer builds of Qt where the forwarding
headers have to be generated before processing the examples project
files.

Change-Id: I683227c97a763c48b8ab090580f37f7134680c59
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>

qtwebengine.pro

-load(qt_parts)
-
 TEMPLATE = subdirs
 
 # The first three subdirs contain dummy .pro files that are used by qmake
@@ -55,3 +53,6 @@ debug.depends: qmake
 
 QMAKE_EXTRA_TARGETS += release \
                        debug
+
+# Move this to the beginning of the project file as soon as we moved to the src layout
+load(qt_parts)